Thermodynamic properties of moisture adsorption in tef (eragrostis tef) seed

The moisture adsorption isotherms of tef (Eragrostis tef) seeds were studied under temperature and relative humidity ranges of 10-40 °C and 15-90%, respectively. The equilibrium moisture content (EMC) decreased with increase in temperature and increased with increase in relative humidity significantly (p < 0.05). The adsorption isotherms exhibited sigmoid shape (type II) which is common for most biological and food materials. The GAB and Peleg models best described the moisture adsorption characteristics of tef seeds resulting in high R2 (0.99), low mean relative percentage deviation, E (<5%) and Root Mean Square Error (RMSE) values with random distribution of residuals. The thermodynamic properties determined in this study were net isosteric heat, differential entropy, spreading pressure, net integral enthalpy and net integral entropy. The net isosteric heats and the differential entropy decreased exponentially with increase in moisture content. The spreading pressure increased with increase in water activity. The net integral enthalpy decreased with increase in moisture content whereas the net integral entropy increased with increase in moisture content and remained negative in value.